The present invention relates to container packages like bottles and jars, for example, glass containers and, more particularly, relates to an improvement in packages of the type wherein a wall portion of a container is, externally and circumferentially, provided with a heat-shrunk thermoplastic cellular member. The present invention is also directed to an improved method for forming such packages.
Recently the packaging industry has successfully developed a package wherein a container, such as, for example, a bottle or jar, which has an upper rim portion defining a mouth opening thereof and a lower portion defining the bottom thereof and including an annular wall joining the rim portion to the bottom portion, is provided, at least along an axial portion of the wall with a heat-shrunk member of a foamed or cellular thermoplastic material in circumferential snug engagement therewith. This member, which is generally in the form of a sleeve, or tubular shape, which circumferentially envelopes at least an axial portion of the wall, provides excellent characteristics to the package and especially to a package wherein the container is a glass container. Such packages are, for example, described in U.S. Pat. No. 3,760,968. Typically these packages are produced by first forming a web, film, or sheet, of a heat-shrinkable, cellular thermoplastic material, by conventional processing, for example, by an extrusion process like a "blown bubble" extrusion process. The process is carried out to provide a heat-shrinking characteristic in the sheet, by a conventional stretching operation, in which the major heat-shrinking, or orientation, or stretching, occurs along the machine direction and only a minor heat-shrinking occurs along the transverse, or cross, direction. The sheet, or web, is also provided, by air cooling, with a skin at each opposed surface of higher density than the central, or core, portion of the cellular web and the depth of the skin on one side is at least about 1.2 times greater than the depth on the other side; these surfaces are smooth, i.e. not roughed up to become fibrillated. This sheet, or film, can then be appropriately provided with a decorative image and the sheet then slit along the machine direction of extrusion to provide rectilinear films, or sheets, which are then employed in forming the package. These rectilinear sheets, or films, are again cut, this time along the cross direction, and then formed into a generally, right cylindrical sleeve with the machine direction of prior forming being the circumferential, or radial, direction of the sleeve and the axial dimension of the sleeve being the previous cross, or transverse, dimension. The reason for this is to provide a more significant circumferential, or radial, shrinkage about the container than an axial shrinkage. Additionally, the sleeve is formed so that the greater skin depth side is the interior surface. Typically, the rectilinear sheet is formed into a sleeve by being brought into contact with a mandrel and the opposed ends of the rectilinear sheet then sealed to each other, such as, for example, in an overlapping relationship by the use of appropriate means, for example, a compressing heat mechanism. The sleeve is then brought into telescopic relation with the container and positioned or located around a wall portion and heat-shrunk to bring it into an annular snug, compressing, engagement with the wall portion of a container. After heat-shrinking, therefore, the sleeve is disposed circumferentially outwardly of the annular sidewall of the container and is in a heat-shrink condition generally disposed at least along a portion of the axial dimension of the sidewalls. Typically, when containers are employed that have a recessed bottom, such as, a concave bottom, the heat-shrunk sleeve includes a lower annular portion extending partially inwardly into the recessed area of the bottom. For further details as to the method of forming such plastic covered containers reference may be had to U.S. Pat. No. 3,767,496 and reference may also be had to U.S. Pat. No. 3,802,942 which discloses suitable apparatus for forming such packages. The three above noted patents are hereby incorporated by reference.
Of course, the container, in addition to having the heat-shrunk member positioned therearound, may be provided with thermoplastic coating materials at various and numerous locations on the container. This concept of employing a heat-shrunk member in combination with various types, and locations, of polymeric coatings is described in co-pending application, U.S. Ser. No. 372,156, filed June 21, 1973.
In the above patents the materials which are taught to be employed to form the rectilinear sheet, or film, which is then formed into the sleeve and heat-shrunk, include polyvinyl chloride, medium or low density polyethylene, polystyrene, "copolymers of carboxylic acid monomers with ethylene (sold under the tradename SURLYN)", cellulose esters, for example, cellulose propionate, butyrate, and acetate, polyamides, and polyurethanes. From a commercial point of view the material which has been found to be most suitable to date has been a closed cellular, general purpose polystyrene material. This material has desirable characteristics, unfortunately however, this cellular polystyrene material is also possessed of certain deficiencies not the least of which include brittleness, relatively easy fracture, poor glass retention when a glass container breaks, and susceptibility to denting, scarring, and tearing, or splitting. When one considers the total process which includes slitting, or cutting, of the material this latter problem is indeed quite significant. These deficiencies of course are reflected in consumer acceptance and also in economies for providing the above packages. The other materials are also possessed of deficiencies.
Attempts to resolve some of the deficiencies of the polystyrene sleeve were made in which a polyethylene layer was provided so that it would be disposed externally of the polystyrene upon application to the container. This approach, likewise, was not entirely satisfactory inasmuch as, for example, poor adhesion of the polyethylene layer to the polystyrene resulted.